"But I think from our enquiries, and the contact we have had with the community, we also know there are other factors - such as gaining street credibility, and gaining respect within the community - that are the prompts for these terrible crimes."

In the first six months of this year, 13 people have been murdered in London in feuds involving black gangsters.

The upsurge of violence has been attributed to the Yardies - criminals who come originally from Jamaica and who have spawned many imitators amongst black British youth.

The original Yardies are Jamaican gangsters

One response has been to extend an intelligence operation called Trident - which has successfully reduced gun crime in Brixton - to London as a whole.

Some critics say that the Met has failed to stem black on black violence because its information network is flawed.

John Brennan, a former detective sergeant, says intelligence is the key.

"For these particular criminals, it is imperative to utilise their friends, because it is a cultural thing that is very difficult to get into," he says.

Although the term Yardie comes from Jamaica, many of the perpetrators of the violence are merely wannabes - black British youth with access to weapons, expensive tastes and cunning.

Police hope poster campaigns will help members of local communities to come forward

"They dress shabbily - jeans, t-shirts and sneakers, like a ragamuffin," says Suzy, an informant who has helped the police in a number of successful operations against so-called Yardies.

"But when they go out on the town, they will dress to a T, drive their Merc, and they'll have probably £10,000 in their pocket to buy the best bottle of champagne and have the prettiest of women and the flashiest of jewellery."

How well the police understand the phenomenon is perhaps less relevant than what they are doing to tackle it.

They hope a poster campaign and a planned London-wide conference will get the support of community leaders.

Patrols by armed response vehicles have been increased, and there is a possibility of a gun amnesty to remove some of the illegally held weapons.